Mechanical properties of Cu/In-48Sn/Cu diffusion-soldered joints

10. SOMMADOSSI S., HUICI J., KHANNA P.K., GUST W., MITTEMEIJER E.J.

ZEITSCHRIFT FUR METALLKUNDE

Año: 2002 vol. 93 p. 496 - 501

0044-3093

Cu/Cu joints were produced in the temperature range 200-360°C by the diffusion soldering process, using the In-Sn eutectic alloy as solder material. Two intermetallic phases (IPs) appeared in the interconnection zone, h (Cu-poor IP) and z (Cu-rich IP) layers, but below 200°C only h grew.  Three mechanical tests were performed to characterize the mechanical behaviour of diffusion-soldered Cu/In-48Sn/Cu joints: the tensile and shear strengths and the (nanoindentation) hardness were measured.  The results show that the z phase has better mechanical properties than the h phase.  The hardness measurements indicate that the most brittle IP layer is the h layer. The h phase has two crystallization morphologies: a duplex microstructure, involving a weak interface between sublayers composed of relatively small grains and relatively large grains, respectively.  The ultimate shear and tensile strengths show similar tendencies for all joints.  The ultimate shear strength of the joints improves almost 3 times when the h phase is converted into the z phase by a solid-solid diffusion reaction process. The surface of the In-48Sn films was etched before the diffusion soldering to improve the mechanical properties.  The resulting joints, if composed of a single z layer, can withstand stresses above 155 MPa.